Intrument lights not working.
Thread Starter
Intermediate
Joined: Jul 2017
Posts: 45
Likes: 0
Intrument lights not working.
I have a real puzzle. I am installing a vintage air AC system in my 1974. I am reinstalling the dash and instrument panels. I wanted to make sure everything is working before I closed it all up. I cannot get the instrument panel lights to work. I don't know anything about automobile wiring circuits. Here is the puzzling part. First thing I did was check the fuse, it is good. Next I used a volt meter to test the circuit. No power at the lamps. So I back tracked to the fuse block. There are two connectors in the fuse block for the fuse. I put the test meter on the fuse and no power there so I removed the fuse again and checked it with the ohm meter. While I had the fuse out I tested the connectors where the fuse is inserted. The one on the right has 12 volts the one on the left has zero volts. Ok, that is normal. But, when I put the fuse back in no power. Zero reading on the voltmeter from either side. If i insert only the end of the fuse in the side with 12 volts I still get 12 volts but if I touch the other end to the other connector the meter goes to zero. I hope that makes sense because I am at a loss to understand this. Why would voltage at the fuse drop to zero when the fuse is inserted? Any help is greatly appreciated
Melting Slicks
Joined: May 2015
Posts: 2,365
Likes: 428
From: Cape Girardeau Missouri
First make certain the IP lamps aren't all the way dimmed. Turn the headlamp **** fully counter-clockwise but not into the detent that turns on the courtesy lights. Next check the TAIL fuse. It feeds the IP fuse by way of the headlamp switch. The IP fuse does not get power until the headlamp switch is pulled out to at least the first notch and again the power comes from the TAIL circuit. With the headlamp switch at the PARK position you should get 12V at one side of the IP fuse with the **** turned fully counter-clockwise. The voltage should drop as you turn the **** clockwise. (Hope I didn't go dyslexic with the direction to turn the ****--if you don't get the proper voltages try the other direction 
)
If both fuses are OK and you get either no voltage reading then the headlamp switch (likely the dimmer) is probably defective. If you get voltage and it seems proper than it sounds like you've lost ground to the lamps. If you continue to get the strange "disappearing" voltage I would again suspect that the headlamp switch is defective--extremely dirty/corroded switch contacts or rheostat wipers can all a meter to detect voltage in an open circuit that disappears as soon as the circuit is closed and attempts to draw current.
)If both fuses are OK and you get either no voltage reading then the headlamp switch (likely the dimmer) is probably defective. If you get voltage and it seems proper than it sounds like you've lost ground to the lamps. If you continue to get the strange "disappearing" voltage I would again suspect that the headlamp switch is defective--extremely dirty/corroded switch contacts or rheostat wipers can all a meter to detect voltage in an open circuit that disappears as soon as the circuit is closed and attempts to draw current.
Thread Starter
Intermediate
Joined: Jul 2017
Posts: 45
Likes: 0
First make certain the IP lamps aren't all the way dimmed. Turn the headlamp **** fully counter-clockwise but not into the detent that turns on the courtesy lights. Next check the TAIL fuse. It feeds the IP fuse by way of the headlamp switch. The IP fuse does not get power until the headlamp switch is pulled out to at least the first notch and again the power comes from the TAIL circuit. With the headlamp switch at the PARK position you should get 12V at one side of the IP fuse with the **** turned fully counter-clockwise. The voltage should drop as you turn the **** clockwise. (Hope I didn't go dyslexic with the direction to turn the ****--if you don't get the proper voltages try the other direction )
If both fuses are OK and you get either no voltage reading then the headlamp switch (likely the dimmer) is probably defective. If you get voltage and it seems proper than it sounds like you've lost ground to the lamps. If you continue to get the strange "disappearing" voltage I would again suspect that the headlamp switch is defective--extremely dirty/corroded switch contacts or rheostat wipers can all a meter to detect voltage in an open circuit that disappears as soon as the circuit is closed and attempts to draw current.
)If both fuses are OK and you get either no voltage reading then the headlamp switch (likely the dimmer) is probably defective. If you get voltage and it seems proper than it sounds like you've lost ground to the lamps. If you continue to get the strange "disappearing" voltage I would again suspect that the headlamp switch is defective--extremely dirty/corroded switch contacts or rheostat wipers can all a meter to detect voltage in an open circuit that disappears as soon as the circuit is closed and attempts to draw current.
